Chapter 2 Section 2
Describing matter

• Matter: anything that has mass and takes up space
– Mass – the amount of matter in something
– Volume – the amount of space something occupies
• Which of the following is matter?
– A car?
– A box?
– You?

• Property: a characteristic of a substance that can be observed

Physical property: a property that can be observed without changing the identity of the substance.
Examples:
• luster
• malleability: the ability to be hammered into a thin sheet
• ductility: the ability to be stretched into a wire
• melting point
• boiling point
• density
• solubility
• specific heat

• Color
• Shape
• Size
• Density
• Melting Point
• Boiling Point

• The physical properties of sodium metal can be observed or measured. It is a soft, lustrous, silver-colored metal with a relatively low melting point and low density.
• Hardness, color, melting point and density are all physical properties.

• Melting point: the temperature at which a substance changes from a solid to a liquid at a given pressure water = 0 o C
• Boiling point: the temperature at which a substance changes from a liquid to a gas at a given pressure water = 100 o C

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• Chemical property: a property that can only be observed by changing the identity of the substance

Chemical Properties
Examples of Chemical Properties
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Reactivity with oxygen
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Nonreactivity with oxygen
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Flammability
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Nonflammability

Chemical Properties

Comparison of Physical and Chemical Properties

• Density is the amount of mass per unit of volume.
• Density can be used to identify a substance.
• The density of water is 1.0g/mL

• Calculations:
D = m/V
• Ex: A cube has a mass of 2.8 g and occupies a volume of 3.67 ml. Would this object float or sink in water?
Mass = 2.8 g Volume = 3.67 mL
D = 2.8g/3.67 mL= 0.76 g/mL
– This object would float in water because its density is less than water (1.0 g/mL).

• Ex: A liquid has a mass of 25.6 g and a volume of 31.6 mL. Use the table below to identify the substance.
M=25.6 g V=31.6 mL
D = 25.6 g/31.6 mL
D= 0.81 g/mL
The substance is ethanol.
Substance
Mercury
Water
Ethanol
Density (g/mL)
13.6
1.00
0.81

Physical Change
Physical change is the change that affects one or more physical properties of a substance.
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Imagine breaking a piece of chalk into two pieces. What are you changing? What is not being changed?
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Physical changes do not change the identity of the matter involved

Physical Change
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Freezing water for ice cubes
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Sanding a piece of wood
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Cutting your hair
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Crushing an aluminum can
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Bending a paper clip
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Mixing oil and vinegar

Chemical Change
Chemical change happens when two or more substance are changed into one or more new substances with different properties.
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Properties of a substance describe which chemical changes will or will not happen
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Chemical change and properties are not the same, a change is the process in which it changes

Chemical Change
Examples of Chemical Changes
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Soured milk
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Effervescent tablets
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Statue of Liberty
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Baking a cake

Chemical Change
Clues that chemical change has occurred
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Changes in color
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Heat
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Fizzing and foaming
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Production of sound or light